This invention relates, generally, to the field of telecommunications including wireless local area networks (WLANs) and, more particularly, to access point (AP) controlled WLAN systems which can facilitate communication directly between two mobile terminals having the same AP.
Wireless local area networks (WLANs), constituted by a plurality of mobile terminals (mobile stations) such as mobile (cell) phones, notebook (laptop) computers which are facilitated with WLAN PC cards, and the like, communicate among themselves as well as through a network server, the network server providing support for communication between mobile terminals in different service sets (service areas) which are associated with different access points (APs). Such networks allow mobile terminals to be moved within a particular service area without regard to physical connections among the mobile terminals within that service area. An example of a model conforming to that developed by the IEEE 802.11 Committee is illustrated in FIG. 9 of the drawings. (Discussion of the IEEE 802.11 model for WLAN architectures is found on pages 442-443 of the text Data and Computer Communications, 5th Ed., by Wm. Stallings, published 1997 by Prentice-Hall, Inc.) Typically, all messages being transmitted among the mobile terminals of the same cell (same AP) in such WLAN schemes must be transmitted to the access point (AP) rather than being directly transmitted between the mobile terminals. Such centralized wireless communication provides significant advantages in terms of simplicity of the communication linkup as well as in power savings. However, such indirect communication between a pair of mobile terminals within a same AP also results in a bottleneck in that AP, noting that all the messages between any two stations within an AP service set must first be received by that AP and then be retransmitted to a destination point. Undesirably, this results, also, in the consumption of valuable communication bandwidth which also leads to an undesirable slowdown, especially when there exists a large number of mobile terminals within an AP service area.
For Direct Mode (DM) communication between two mobile terminals (MTs) in access point (AP) controlled WLAN systems to be successful, both MTs (1) have to be able to support DM, (2) they have to be associated to the same AP and (3) be able to create a wireless radio link with feasible (i.e., satisfactory) transmission power level. However, an underlying problem has existed in achieving this. Namely, there has been a problem of how the MTs as well as the associated AP know with certainty whether both of those MTs can have a DM radio linkup with a satisfactory transmission level prior to completion of the DM connection setup. (Direct Mode [DM], as referred to in the present application, means a Direct Mode communication linkup in which a direct or straight communication is effected between two MTs within the same AP service set of an AP controlled WLAN system.) Further, there has also been an underlying problem of how the initiating MT is able to create a DM connection to a remote, second MT of the same AP service area since the local unique identifier (LUI), which is generated by the AP to identify each MT associated with that AP, is not known by the other, remote MT. Any attempt at overcoming these problems must necessarily consider the following related issues: complexity, security, processing resources as well as channel usage.
The calibration scheme proposed by Sony International Europe as HL14SON2a, in the ETSI EP Bran (European Telecommunications Standards Institute EP Broadband Radio Access Network) No. 14 Conference, on July 1999, and incorporated herein reference, is based on a topology map stored in the AP computer which is to be used for finding out which MTs associated with that AP are feasibly located to permit DM communication. Such a topology map as that featured in HL14SON2a, July 1999, is presently illustrated as reference numeral 100 in FIG. 10 of the drawings with regard to a showing, in the discussion which follows, of the impracticality as well as the security concerns that would be raised in using such a topology map to effect a DM communication setup between two MTs.
The basic concepts of the Standard, as previously proposed in HL14SON2a, is to ascertain the network topology associated with an AP via a calibration mechanism. Each MT associated to the same AP, according to that proposal, performs received signal strength (RSS) measurements with respect to all other ones of the MTs of that AP and reports them to the AP. Once all MTs have reported their measurement results to the corresponding AP, the AP creates and stores a topology map of that network. Such a topology map as that illustrated in FIG. 10 of the drawings indicates the quality and connectivity between each MT with all other MTs associated with the same AP. Based on such a connectivity map as that illustrated in FIG. 10 of the drawings, a connection setup for a Direct Mode (peer-to-peer) session can be performed through coordinating the three key elements, namely, the two MTs which are to be included in DM connection as well as the associated AP. In order to facilitate such a radio communication hookup, the example given in HL14SON3A, also presented in the ETSI EP BRAN No. 14 conference of July 1999, is applicable in connection with achieving a regulated transmit power level for each MT, independent of the transmit power associated with the other MTs of that AP. The HL14SON3A proposal submitted in connection with the HIPERLAN/2 Standard is also incorporated herein by reference.
Regarding the addressing problem, referred to earlier, no solutions have yet to be proposed which are directed, especially, to DM communication in AP controlled WLAN systems, based on the inventors"" knowledge. Also, the typical way of distributing data in WLAN systems is to broadcast information for all MTs periodically or to maintain a mapping list from the local unique identifiers (LUIs) which correspond to the higher layer addresses associated with each AP. (The higher layer addresses are typically internet protocol (IP) addresses or Ethernet addresses, mobile phone numbers, and the like.) In the above-noted HL14SON2a proposal (HIPERLAN2 proposed Standard), there exists a master/slave situation, in which the AP is always the master and MT is the slave. Since AP is dynamically associating/disassociating medium access control identifiers (MAC-Ids) to joining/leaving MTs, it becomes paramount, at least for security reasons, that the AP should be the only entity or player in any communication linkup within the network which has specific knowledge about the MAC-Id mapping within its cell. Spreading or loosely channeling such information to the MTs poses questions of the security of the network. To avoid such problem, only MTs which are assigned to the same cell (same AP) and which are involved in DM communication linkup, the inventors submit, should actually have the right to ask for the corresponding MAC-Id address of another MT in order to initiate a DM connection.
Considering that the information is being broadcasted via wireless radio channel, the topology map (as proposed in HL14SON2a) as well as the broadcasting of the addressing information (from the higher layer address associated with the corresponding MAC-Id) have a bottlenecking effect on channel usage. Such negative impact on channel usage is especially evident during the periodic calibration phase. Since not all of the MTs may support DM communication and since DM communication is effected rather infrequently (e.g., once per hour, maybe), broadcasting of the RSS and addressing information as well as effecting the calibration within a period which is short enough for purposes of updating the data has a deleterious effect on the capacity of the radio channel during such times.
With regard to the topological map shown in FIG. 10 of the drawings, which relates to the Sony contribution of the Standard proposal of HL14SON2a, mentioned above, an updating mechanism is available for regularly changing (updating) the received signal strength (RSS) measurements performed among the different MTs. The purpose of such mapping of the RSS of the local MAC-Id addresses is to have some means to quantify an actual updated list of the actual signal strength situation among the different MTs serviced by the same cell (same AP). According to such a scheme, an AP maintains a priori knowledge about the possibility of DM connection setup between two MTs. Referring to FIG. 10, RSS 23-1 represents the received signal strength at the mobile terminal having the MAC-Id3 address, of a message transmitted by the mobile terminal having the MAC-Id1 address. On the basis of such values held in such topological map, the AP can decide whether DM connection of a pair of MTs results in the feasible wireless radio link.
Although valuable information may appear to be contained in such a topological map, there are a number of drawbacks/hindrances that must be overcome if a practical and efficient DM linkup is to be effected. Among such drawbacks are the following:
(a) The reliability of the RSS values in the wireless indoor environment is unpredictable. Namely, if the MT is moving only slightly, especially, inside a building site, the current situation pertaining to the RSS values between that MT and all other MTs of the same cell may completely change (i.e., deep fading is observed, or the line of site (LOS) path between two MTs may no longer exist, etc.). Therefore, the RSS values in such a case, would not constitute a reliable information source even under a regular, periodic updating of the topological map. Under such conditions it would also not be reliable to effect an accurate characterization of an indoor channel in terms of the RSS level among the different MTs. As another example regarding the unreliability of the attained RSS values in an indoor environment, even if the RSS measurements have been recently updated, they are still unreliable. That is, while the mobile phone is laying on an office table somewhere in the building, the RSS measurements directed thereto have one set of values. However, when the user picks up the mobile phone from the table and dials the destination number, it is quite probable that the RSS signal measured under this condition would be totally different from the recently measured RSS value when the mobile phone was still on the table. For instance, the wavelength for 5 GHz carrier is about 6 cm. Therefore, any slight movements of the MT would result in a significant phase change and deep fading (e.g.., several dBs) could be observed due to occurrence of a multi-path propagation effect.
(b) In order to maintain a regular updating of the topological map, a great deal of information exchange is required that would have no relevance to a particularly desired DM connection to be effected. That is, even the inactive/powered down MTs must perform RSS measurements periodically in order to maintain a regularly updated topological map in the AP. Such has a wasting effect on the scarce channel resource available during a DM connection setup as well as during DM operation.
(c) In order to perform the RSS measurements required by the topological map, it is observed that all of the MTs have to know the MAC-Ids of all other MTs serviced by the same AP, in order to be able to identify the MT with which it performs any RSS measurements. However, since the AP is also updating the mapping table in the case a new MT is joining the cell or an old one is leaving the cell, the addressing task places an even greater burden on the network as well as becoming rather complex. As stated earlier, the exchange of MAC-Ids between the AP and all of the MTs, periodically, may lead to a security issue.
It is an object of this invention to realize a Direct Mode communication between two mobile terminals (MTs) in access point (AP) controlled WLAN systems as efficiently and economically as possible.
It is also an object of this invention to realize AP controlled WLAN systems featuring Direct Mode communication between two mobile terminals within the same cell (same AP) as an optional linkup to that conventional/standard modes of WLAN communication.
It is a further object of this invention to realize a DM communication scheme between two MTs in AP controlled WLAN systems which is reliable and which avoids unnecessary waste of the scarce channel resource.
It is a still further object of this invention to realize a DM communication scheme between two terminals in AP controlled WLAN systems which avoid broadcasting information which is unnecessary for effecting a DM connection and thereby avoiding matters pertaining to security issues. (Security issues would likely result through an unnecessary exchange of local unit identifier addresses pertaining to the individual MTs of each AP.)
It is also an object of this invention to realize a DM communication scheme between two mobile terminals in AP controlled WLAN systems having reduced power consumption requirements as well as reduced waste of channel space.
The foregoing and other problems are overcome and the objects of the invention are realized through effecting AP controlled WLAN systems featuring DM communication between two mobile terminals serviced by the same AP, in accordance with the examples illustrated in the drawings and described in the specification.
Briefly, the invention features a method for Direct Mode communication between two mobile terminals in access point (AP) controlled WLAN systems. Such a DM scheme calls for (a) establishing that an initiating, first mobile terminal and a remote, second mobile terminal are associated to a same AP; (b) establishing that the remote, second mobile terminal supports a DM operation feature as does the initiating, first mobile terminal; (c) sending, by the AP, address identifiers of the first and second mobile terminals to the second and first mobile terminals, respectively, including granting of a frequency-power resource slot to each of the two mobile terminals to initiate received signal strength (RSS) measurements between the two mobile terminals; and (d) sending, to the AP, RSS measurements performed by the first and second mobile terminals of mobile terminal identifier messages (which are xe2x80x9chelloxe2x80x9d messages) sent to them by the second and first mobile terminals, respectively. DM communication between the first and second mobile terminals continues with exchange of information to conclusion when a mobile terminal identifying message is satisfactorily received by both mobile terminals and when a mobile terminal identifying message of either of the two mobile terminals is not satisfactorily received, DM communication setup is terminated. Under such condition, the AP can be requested to effect a communication linkup between the two mobile terminals using known/standard WLAN routing schemes, in which case the exchange of information would also flow to the AP.
In accordance with the present invention, an MT-initiated DM communication setup as well as an AP-initiated DM communication are possible. An MT-initiated DM connection can be effected in the case the initiating MT knows beforehand that the remote mobile terminal is associated to the same AP. The AP has a mapping table, kept in its database, of the local unique identifiers (which includes the MAC-Id, as one example) of each MT in its cell along with the corresponding higher layer protocol address associated therewith (e.g., Ethernet address, IP address, mobile phone numbers). The AP database also contains information of the DM capability of the MTs associated with that AP. Therefore, the AP is able to check its database to determine whether or not the remote MT is able to support a DM connection. If the remote, second MT supports a DM connection, it then can decide whether it wants to initiate DM linkup with the initiating, first MT. As to the AP-initiated DM scheme, the initiating, first MT does not know whether or not the remote, second MT is associated to the same AP and whether it is also DM capable. Accordingly, the initiating MT just sends a connection request to the AP with the corresponding higher layer protocol address of the destination. Consulting the database, the AP gives notice that the remote MT is also located in the same cell. From this point on, the AP initiates DM similarly as that in the MT-initiated DM communication setup scheme.
The DM connection scheme according to the present invention simplifies the current available scheme, for example, in ETSI EP BRAN (European Telecommunications Standards Institute Europe Broadband Radio Access Network) for Direct Mode (DM), as it pertains to the recent proposal for the HIPERLAN/2 Standard, July 1999. In accordance with the present invention, only two mobile terminals (MTs) and the associated access point (AP) are involved in any current DM communication setup and performance. All activity as it is related to an updating of a topological map (e.g., signaling), such as featured in the Sony proposal in HL14SON2a, July 1999, for the HIPERLAN/2 Standard, and as explained with regard to FIG. 10 of the present application, is avoided. Further, full updating of the mapping table does not involve in the broadcasting of local unique identifiers (LUIs) such as local MAC-Id addresses, although not limited thereto. Only the two MTs which are involved in any current DM connection setup receive information about each other from the mapping table. Also, power consumption as well as unnecessary waste of channel space, such as results in the topological map according to the above-noted proposal for the HIPERLAN Standard, is avoided. Additionally, the present DM communication setup scheme can be easily facilitated without too many complexity concerns.